The invention applies to the fields of medical technology and laser technology and relates to dialyzers as they can be used, for example, for hemodialysis and ultrafiltration, and to a process for modifying these dialyzers by means of a laser.
Capillary hollow membranes have been used for a long time for liquid-phase permeation, in particular hemofiltration and ultrafiltration. These hollow membranes can be made of various materials, for example, cellulose.
Such hollow membranes are bound together into bundles and are inserted into a cylindrical filter body, the dialyzer. Subsequently, both ends of the bundles are fixed in the dialyzer using a plastic. Various plastics can be used here. This fixation seals the dialyzer and, at the same time, seals the hollow membranes off from the dialyzer. The protruding plastic in which the ends of the hollow membranes are embedded is removed using a multi-step cutting process so that the ends of the hollow membranes are uncovered again.
U.S. Pat. No. 5,814,179 describes in detail the prior art concerning the manufacture of dialyzers and the demands placed upon them, and the problems in the manufacturing process. The emphasis of the content is the improvement of the effectiveness of the membrane effect of the embedded hollow membranes. The uncovering of the hollow membranes occurs by means of a mechanical cutting process (WO 98/28065 A1). Thus, the quality of dialyzers and, in particular, the quality of the cut surfaces with the entrance and exit openings of the hollow membranes, depends solely on the quality of the mechanical cut that can be achieved.
As a rule, for one cutting process, at least 2 rough cuts and 2 precision cuts are needed at each dialyzer end. In this connection, a different knife is used for each cut, i.e., eight knives are necessary per system. Hardened steel knives with a double ground edge and a lapped bevel are used. The service life of the knives differs; it lies between 10 and a maximum of 3000 cuts per knife. For each changing of a knife, the system must be stopped. Thus, standstill periods occur often. These standstill periods furthermore change the cutting result in a negative fashion because of the continuing hardening of the plastic.
During the cutting process, the cutting direction runs perpendicular to the lengthwise axis of the hollow membrane; there are no lateral cutting force components like in the case of an agitated circular cut. The clearance angle of the knife must be selected to be as small as possible in order to prevent a cutting force component parallel to the hollow membrane and therefore a pulling out of the hollow membrane. However, small clearance angles often cause a sliding of the free surface of the knife on the plastic as a result of an elastic resilience and thus a resulting damage to the cutting surface due to friction.
After the final cut, the plastic must have a microscopically smooth surface (FIG. 1). In this situation, the hollow membranes may not be damaged or detached from the plastic. During use, even slight damage to the surface of the hollow membrane ends can lead to injuries of the red blood cells and thus to blood clotting. In order to fulfill these high demands, the cutting knives that are used are replaced often. Nonetheless, the reject rate is very high.
The object of the invention is to reduce the standstill periods during the processing of the dialyzer ends and to achieve a smooth surface of the dialyzer ends.
The object is attained by the invention specified in the claims. Further embodiments are the object of the subclaims.